如题:

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string a, b;
    cin >> a >> b;
    

    int counter = 0;
    bool flag = true;
    if (a.size() >= b.size())
    {
        for (int i = 0; i < a.size(); ++i)
        {
            if (a[i] == b[counter])
            {
                counter++;
                if (counter == b.size())
                {
                    cout << b << " is substring of " << a;
                    flag = false;
                    break;
                }
            }
            else
                counter = 0;
        }
    }
    else if (b.size() > a.size())
    {
        for (int i = 0; i < b.size(); ++i)
        {
            if (a[counter] == b[i])
            {
                counter++;
                if (counter == a.size())
                {
                    cout << a << " is substring of " << b;
                    flag = false;
                    break;
                }
            }
            else
                counter = 0;
        }
    }
    if (flag)
        cout << "No substring";

}